1. Field of the Invention
This invention is in the field of non-destructive testing utilizing fluorescent magnetic particles, the particles including a daylight fluorescent pigment and a cascading opacifier attached to a ferromagnetic particle core of such size that the particles can be used for magnetic inspection processes under simultaneous illumination by ultra-violet light and white light.
2. Description of the Prior Art
Magnetic particles have been used for flaw detection in magnetizable workpieces for many decades. More recently, the magnetic particles have been combined with fluorescent particles either in the form of a water or oil suspension whereupon the workpiece was inspected under filtered ultra-violet or black light to observe any concentration pattern of fluorescent particles caused by a surface discontinuity. Prior art patents referring to this type of inspection technique include Switzer U.S. Pat. No. 2,267,999 and Kazenas U.S. Pat. No. 3,936,287. These patents relate, respectively, to lacquer bonded and resin bonded fluorescent magnetic particles for use in this type of inspection process.
Methods of making fluorescent coated magnetic particles have also been described in my previous U.S. Pat. No. 3,404,093 and in U.S. Pat. No. 3,485,758 in which James S. Borucki was a co-applicant.
One of the principal areas of application of the fluorescent magnetic particle inspection process is that of steel billet inspection. In this type of inspection, the billet is inspected for longitudinal seams, and the fluorescent magnetic particle inspection takes place under black light in a darkened inspection area. Many billets, however, contain corner tears or other imperfections that because of their large size or orientation to the magnetic field do not produce indications, and cannot be seen in the dark. Consequently, the location of such imperfections has required a separate inspection in visible light.